If you have
with foo.svg having a percent-valued height and/or width on its root <svg> node, then the image isn't drawn.
(It looks like we might treat it as if that dimension were 0px, and we honor the other dimension. For example, if you have width=50% height=200px, then the list items end up being about 200px apart vertically, even though no image is drawn.)
See also Tab Atkins' discussion of the spec vs. various browsers' behaviors in this thread:
(When he mentions Firefox there, I suspect he's referring to 3.6 or another version from before SVG-as-an-image support was added.)
I'd think the patches in bug 611099 ought to fix this, since they remove the concept of percent intrinsic size.